The present invention relates in general to detecting misfires in internal combustion engines for automotive vehicles, and, more specifically, to a circuit and method for integrating ion current to detect misfires.
Automobiles employ catalytic converters to reduce the amount of pollutants in the engine exhaust. However, when a cylinder misfires so that no combustion or incomplete combustion occurs, uncombusted fuel is introduced into the exhaust which burns in the hot catalytic converter. The heat from fuel burning in the catalytic converter destroys the catalyst. Thus, it becomes desirable to detect and count engine misfires and to inform the operator of the vehicle upon occurrence of excessive misfires so that steps may be taken to protect the catalytic converter. Gasoline turbocharged direct injection (GTDI) engines can be especially vulnerable to misfires at high loads and RPM.
It is also desirable to detect misfires in order to allow adaptive control of the combustion engine in order to improve engine performance or to possibly eliminate the condition leading to misfire or remove fuel to the misfiring cylinder and thereby protect the engine. The identity of a misfiring cylinder and the frequency of misfires is typically recorded for later use during diagnosis and repair of the vehicle.
It is known to monitor crankshaft acceleration in order to detect misfires, but known methods can be ineffective for hybrid electrics vehicles and for vehicles with dual mass flywheels, for example.
Another method for detecting misfires monitors an ion current flowing across a spark plug after occurrence of an ignition spark. The more complete the combustion, the greater the conductance of the combustion products and the greater the ion current that flows. Integrating the area under the ion current signal for a certain amount of crank angle degrees after spark is considered to be a reliable indicator of misfire and late burns, but conventional implementations have been expensive and require an extra signal wire to connect each ignition coil directly to the powertrain control module (PCM), additional analog-to-digital converter inputs in the PCM microprocessor, and software to integrate the area under the ion current curve in real time. It would be desirable to integrate the ion current in a manner that requires no additional inputs to the PCM and minimizes the need for any additional software (e.g., for integrating the ion current).